Two- and three-way chemometrics methods applied for spectrophotometric determination of lorazepam in pharmaceutical formulations and biological fluids

In this work, direct determination of lorazepam, an anxiolytic and sedative agent, in pharmaceutical formulations and biological fluids (urine and human plasma) was accomplished based on ultraviolet spectrophotometry (260-380 nm) using parallel factor analysis (PARAFAC) and partial least squares (PLS). The study was carried out in the pH range from 1.0 to 12.0 and with a concentration range from 0.50 to 8.75 μg ml−1 of lorazepam. Multivariate calibration models using PLS at different pH and PARAFAC were elaborated for ultraviolet spectra deconvolution and lorazepam quantitation. The best models for the system were obtained with PARAFAC and PLS at pH = 2.05 (PLS-PH2). The capabilities of the method for the analysis of real samples were evaluated by determination of lorazepam in pharmaceutical preparations and biological (urine and plasma) fluids with satisfactory results. The accuracy of the method, evaluated through the root mean square error of prediction (RMSEP), was 0.0429 for lorazepam with best calibration curve by PARAFAC and 0.0467 for lorazepam with PLS model at best pH. The protolytic equilibria of lorazepam at 25 °C and ionic strength of 0.1 M have also been determined spectrophotometrically. Protolytic equilibria of lorazepam were evaluated by DATAN program using the corresponding absorption spectra-pH data. The obtained pKa values of lorazepam are 1.54 and 11.61 for pKa1 and pKa2, respectively.